Air-Conditioner Control

ABSTRACT

The invention provides an air-conditioner for maintaining a temperature of a conditioned space at or near a set temperature. The air-conditioner comprises at least one rotating or reciprocating element adapted to rotate or reciprocate at a variable frequency. The variable frequency including one or more nuisance frequencies at which vibration or noise within the air-conditioner or the conditioned space causes a nuisance. A processor (30) programmed to control variation of the variable frequency in response to operational requirement. The processor is configured to operate the at least one rotating or reciprocating element so as to substantially exclude operation at the one or more nuisance frequencies.

FIELD OF THE INVENTION

The present invention relates to air conditioners, in particular to anew control system and method in relation to air-conditioners whichreduces nuisances caused by vibration. The invention has particularapplication to air-conditioners in recreational vehicles, but is morebroadly applicable to air-conditioning in general.

BACKGROUND OF THE INVENTION

Many modern air-conditioners use inverter technology to control thespeed of the compressor motor to drive a variable refrigerant flow. Inthis regard, traditional air-conditioners use a compressor whichoperates at a single speed and is switched on or off to control thetemperature of the conditioned space. On the other hand, more modernair-conditioners use inverter technology having a variable frequencydrive that controls the speed of the motor and thus the compressor andtherefore the heating and cooling output of the air-conditioner.

Inverter technology has become common place due improved efficiency andsmooth operation of air-conditioners with a reduction in costs ofcontrolling electronics. However, because the compressor can now beoperated over a wide range of frequencies, potential problems of noiseand fatigue due to vibration may be exacerbated. While sources ofvibration can be eliminated by damping or de-tuning equipment away fromresonant frequencies with a compressor working at a constant speed, itcan be difficult to identify all sources of vibration over a wide rangeof driving frequencies of the compressor of an inverter system. Ananalogous problem may occur with continuous control of fan speed, wherea fan can be a source of vibration particularly in relation to annoyingnoises transmitted through cladding.

Vibration problems may be particularly difficult to overcome insituations where the mounting of the air-conditioner is in a wall orroof having relatively flexible construction. For example in arecreational vehicle, a roof mounted air conditioner can generatesympathetic resonant vibrations in the roof structure or otherstructural or cladding of the vehicle often located quite a distancefrom the air-conditioner. Noise from such vibrations can be particularlyannoying to occupants and the resonant frequencies are beyond capabilityof prediction, occurring differently on a case-by-case basis dependingon construction of the particular vehicle and its customisation. Once anair-conditioner is installed, there may be little that the techniciancan do to solve the problem with prior art inverter air-conditioners.

It is an object of the present invention to overcome or ameliorate atleast one of the disadvantages of the prior art, or to provide a usefulalternative.

SUMMARY OF THE INVENTION

In accordance with a first broad aspect of the invention there isprovided an air- conditioner for maintaining a temperature of aconditioned space at or near a set temperature, the air-conditionercomprising:

at least one rotating or reciprocating element adapted to rotate orreciprocate at a variable frequency, the variable frequency includingone or more nuisance frequencies at which vibration or noise within theair-conditioner or the conditioned space causes a nuisance; and

a processor programmed to control variation of the variable frequency inresponse to operational requirements;

wherein the processor is configured to operate the at least one rotatingor reciprocating element so as to substantially exclude operation at theone or more nuisance frequencies.

In one embodiment, the at least one rotating or reciprocating elementcomprises a variable frequency compressor supplying correspondingvariable compressive power. The processor may comprise an adjustmentcapability allowing reconfiguring to substantially exclude operation atone or more of the nuisance frequencies that are identified aftermanufacture of the air-conditioner. The adjustment capability may allowreconfiguring to substantially exclude operation at one or more of thenuisance frequencies that are identified after installation of theair-conditioner.

In one embodiment, the processor is adapted to operate the at least onerotating or reciprocating element at a set of allowed frequencies whichdo not include any of the one or more nuisance frequencies and to causetransition between the allowed frequencies in response to theoperational requirements. The transition may be a programmed gradualtransition between the allowed frequencies over a transition time,avoiding operation at or within the nuisance frequencies for more than amaximum time during the transition. The maximum time may be less than 20seconds, less than 10 seconds or less than 5 seconds.

In one embodiment, the processor is adapted:

to compute a target frequency for sustained operation according to theoperational requirements;

to compute a revised target frequency by increasing or decreasing thetarget frequency if required to avoid the one or more nuisancefrequencies; and

to operate the at least one rotating reciprocating element at therevised target frequency.

The processor may be adapted to increase the target frequency ifrequired to avoid the one or more nuisance frequencies if a rate ofchange of temperature difference from a temperature set point indicatesmore power is required, and to decrease the target frequency if requiredto avoid the one or more nuisance frequencies if the rate of change oftemperature difference from a temperature set point indicates less poweris required.

In one embodiment, the adjustment capability is provided by a capabilityof user to edit or add to a list of the one or more nuisance frequenciesstored in a non-volatile memory.

In one embodiment, the processor comprises a nuisance frequencydetermination mode whereby the processor operates the rotating orreciprocating element at one or more specific frequencies to allowobservation or measurement of whether the nuisance occurs during theoperation at each of the one or more specific frequencies. When in thenuisance frequency determination mode, the processor may be furtheradapted to receive input by the user of the observation or measurementand to update the list of the one or more nuisance frequencies stored inthe non-volatile memory.

In one embodiment, the at least one rotating reciprocating elementcomprises a rotating fan configured to supply conditioned air or to passair over a heat exchanger.

In one embodiment, the air-conditioner is implemented on a recreationalvehicle.

According to a second broad aspect of the invention there is provided amethod of reducing a nuisance caused by an air-conditioner, theair-conditioner being adapted to maintain a temperature of a conditionedspace at or near a set temperature, the air- conditioner comprising:

at least one rotating or reciprocating element adapted to rotate orreciprocate at a variable frequency, the variable frequency includingone or more nuisance frequencies at which vibration or noise within theair-conditioner or the conditioned space causes the nuisance; and

a processor programmed to control variation of the variable frequency inresponse to operational requirements;

the method comprising the step implemented in the programmed processorof operating the at least one rotating or reciprocating element so as tosubstantially exclude operation at the one or more nuisance frequencies.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are cross-sectional views from two directions of arecreational vehicle air-conditioner having an external unit and aninternal air distribution box and user interface;

FIG. 2 is a functional block diagram of the air-conditioner FIG. 1showing control elements according to an embodiment of the currentinvention;

FIG. 3 is a graph of frequency versus time illustrating a controlscenario according to an embodiment of the current invention inconjunction with the accompanying description;

DETAILED DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the drawings, thesame elements are denoted by the same reference numerals throughout. Inthe following description, detailed descriptions of known functions andconfigurations incorporated herein have been omitted for conciseness andclarity.

Referring initially to FIGS. 1A and 1B showing side and end crosssectional views respectively, a typical air-conditioner system to whichthe invention is applied comprises an external rooftop unit 10 housing acompressor, heat exchangers and fans installed above an aperture in aroof 1 of a recreational vehicle, exchanging return and supply airthrough internal componentry 3 attached to 2 ceiling 2, the internalcomponentry 3 comprising an air distribution box and user communicationsinterface.

Referring now to FIG. 2, a functional block diagram is shown wheredotted lines indicate communication or control connection. Theair-conditioner comprises principal components of compressor 20,external air heat exchanger 21 and fan 22, conditioned air heatexchanger 23 and fan 24, system processor 30, non-volatile memory 31,and conditioned space temperature sensor 33, and user communicationsinterface 32. Compressor 20 pumps heat between heat exchanger 21 and 23in one or both directions to provide the heat transfer between anexternal air blowing by external air fan 22 and conditioned aircommunicating with an internal space by conditioned air fan 24. As isknown in the art, compressor 20 (for example Boyard KFA-102Z220) isdriven by an AC motor controlled by a frequency control system to varythe speed (or frequency of rotation) of the compressor 20 motor. Systemprocessor 30 is typically based on a microprocessor and is responsibleamong other functions for sending commands to a frequency control systemof compressor 20 to control the frequency of the compressor 20 inresponse to air-conditioner demand in order to maintain a desiredtemperature set point, having regard also to other parameters such asmaximising performance or efficiency. The temperature set point istypically selected by an internal occupant through user communicationsinterface 32 communicating with a hand-held remote control 34. Nuisancesmay be caused by vibrations occurring as a result of operation of themoving components compressor 20, external air fan 22, or conditioned airfan 24 or a combination thereof. Noise or vibrations may occur withinthe unit or outside the unit as described above.

As is known in the art, system processor 30 will increase or decreasethe frequency of the compressor and hence the power output of theair-conditioner in step with a difference of the internal airtemperature measured through the temperature sensor 33 and the setpoint. Typically, the greater the difference between the measuredtemperature and the set point, the greater the desired power andtherefore the frequency of the compressor 20.

According to the invention, system processor 30 is programmed tosubstantially exclude operation at one or more compressor frequencieswhich produce a vibration nuisance. The system processor is alsoprogrammed to substantially exclude operation at one or more rotationalfrequencies of the external air fan 22, or conditioned air fan 24. Thesefrequencies hereinafter shall be called nuisance frequencies.

The nuisance frequencies within the air-conditioner itself may bedetermined by the manufacturer in the design phase. One method ofdetermining nuisance frequencies within the air-conditioner itself is torun the compressor 20 and/or the external air fan 22 or the conditionedair fan 24, over a range of frequencies from a minimum to a maximum insmall increments such as 1 Hz, dwelling for a sufficient period at eachfrequency (such as 10 to 20 seconds or more) and measuring for excessivevibration or noise. The measurement may be made by a vibration sensor,microphone or combination of the two, or by human operator observation.While one obvious source of a nuisance frequency is a frequency ofresonance of the refrigerant tubes attached to the compressor, typicallyat a low frequency around 30-35 Hz, there can be other higherfrequencies containing islands of nuisance frequencies which causevibrations or noise in other parts of the air-conditioner.

Nuisance frequencies occurring in an end customer installation can bedetermined in situ by similarly running the compressor 20 and/or theexternal air fan 22 or the conditioned air fan 24, over a range offrequencies as described above in the installed environment andmeasuring or listening for excessive or annoying vibration or noiseemanating from anywhere in the installed environment. In therecreational vehicle application, nuisance frequencies may be determinedin a test installation in a new model of recreational vehicle beforemarket release, or may be determined after market after installation foran end customer by a technician or by the end customer when individualproblems arise.

In this embodiment, system processor 30 may be switched by an operator(which may be a technician or an end customer) into a nuisance frequencydetermination mode which implements the above incremental scan in stepsbetween a minimum and maximum. Identified nuisance frequencies mayconveniently be recorded in the non-volatile memory 31 by the operatorover the communications interface 32 such as by pressing a “select”button on the remote control 34 when a nuisance is noted during thescan. There may be a range of adjacent scanned frequencies over which anuisance remains, in which case each of the adjacent scanned frequenciesrepresenting a forbidden band is recorded as a nuisance frequencytogether representing a forbidden band of nuisance frequencies (forexample 65 Hz, 66 Hz, 67 Hz if the step size between tested frequenciesis 1 Hz).

In simpler embodiments, system processor 30 may be switched into amanual mode allowing the technician or end customer to manually increaseand decrease the compressor and/or the external air fan 22 orconditioned air fan 24, frequencies to note down the identified nuisancefrequency or frequencies from a display or other communication of thecurrent compressor frequency.

With one or more nuisance frequencies identified, in this embodimentsystem processor 30 may be configured or reconfigured, by reprogrammingor data table adjustment, to avoid sustained operation at the nuisancefrequencies during operation, or at newly identified nuisancefrequencies particularly in the case of end customer problems.Reconfiguration may occur automatically when the user presses the selectbutton as described above and the system adds the current frequency tothe list of nuisance frequencies stored in the non-volatile memory.

Referring now to FIG. 3, there is shown a graph of frequency versus timein an example of operation of the system. In this example, the systemprocessor has been operating the compressor at frequency F1 for asustained period before time T1 and then at time T1 the system processortakes a measurement of the actual temperature of the conditioned spaceand calculates the difference ΔT between the actual temperature and theset point. In the case where the difference ΔT has increased compared toa previous time point, an appropriate response of the system processormay be to increase the cooling output and therefore the speed of thecompressor to a higher allowed target frequency F2. The transition fromF1 to F2 is effected by commands to the frequency control system ofcompressor 20 bringing about a gradual increase from F1 to F2 (forexample 1 Hz per second increase). At time T2, higher frequency F2 isreached. After a predetermined interval of sustained operation (such as2 minutes after T2), at time T3 a further measurement of ΔT is made, anda programmed decision made whether to adjust the target frequencyfurther. In this example the decision is made to stay at frequency F2for a further predetermined interval (such as two minutes after T3).Persons skilled in the art will understand that many and varied controlalgorithms are known to control temperature around the set point byperiodically testing the temperature difference ΔT and adjusting theresponse in terms of selecting a target frequency at which to operatethe compressor. Some such control algorithms are adaptive self-learningalgorithms, and some are non-adaptive with fixed parameters. Typically,there is a programmed relationship where target frequency increases withtemperature difference T. The programmed relationship may vary dependingon whether the temperature difference ΔT is increasing or decreasing inorder to avoid hunting or overshoot. Further, the programmedrelationship may vary depending on other operational requirements suchas different modes selected by the user as are known in the art tooptimise for economy, power or quiet operation.

In the invention, the processor is programmed to substantially excludeoperation at any of the one or more nuisance frequencies. While it isinevitable that a nuisance frequency may be briefly visited while thecompressor speed is being ramped up from a frequency lower than anuisance frequency to a target frequency higher than a nuisancefrequency, such as in the example above if a nuisance frequency liesbetween F1 and F2, the invention avoids the system processor fromdwelling at the nuisance frequency for any substantial amount of timeand causing significant sustained nuisance. Periods of brief visitationare usually able to be restricted to one second or less, but maximumtimes of five seconds 10 seconds or 20 seconds are allowable if thecircumstances dictate.

Avoidance of the nuisance frequencies may be achieved in a number ofways.

EXAMPLE 1

In one embodiment, a discrete set of allowable frequencies F1, F2 . . .FN is used for sustained operation between decision times, the allowablefrequencies having values which do not include any of the nuisancefrequencies. The system processor 30 operates to control the frequencyby transitioning between the allowable frequencies at the decisionpoints such as T2 and T3 above. In this technique, one way ofreconfiguring the system after installation is to edit the values of theallowed frequencies F1, F2 . . . FN held in non-volatile memory ratherthan to explicitly store a list of nuisance frequencies in non-volatilememory.

EXAMPLE 2

Another embodiment utilises a control algorithm which first computes atarget frequency at decision points such as T2 and T3 above based onoperational requirements without regard to the nuisance frequencies, andthen to compute a revised target frequency by increasing or decreasingthe target frequency if required to avoid one of the nuisancefrequencies. The air-conditioner is then operated at the revised targetfrequency for the sustained period (typically two minutes in the exampleabove) until the next decision point. Typically, the target frequency isrevised by as small as possible an amount to avoid the nuisancefrequencies, and in an appropriate direction. For example, if the rateof change of temperature difference ΔT indicates a widening gap and thatmore power is required, the appropriate revision may be an increase andconversely a decrease if the rate of change of temperature differenceindicates a lessening gap.

By providing a system and method which is specifically designed to avoidsustained operation at nuisance frequencies, which in embodimentsdescribed above may involve reconfiguring after installation, animproved air-conditioning is provided with reduced nuisance fromvibration or noise.

Persons skilled in the art will also appreciate that many variations maybe made to the invention without departing from the scope of theinvention, which is determined from the broadest scope and claims.

For example, while the description above is primarily concerned withoperation of the compressor 20, analogous avoidance of nuisancefrequencies caused by either fan 22 or 24 can be dealt with similarlyand is within the scope of the invention.

In the claims, the term “substantially exclude operation at the one ormore nuisance frequencies” encompasses operation which allows thetransitory operation described above involved in a gradual transitionfrom operation at one frequency to another.

In the claims which follow and in the preceding description of theinvention, except where the context requires otherwise due to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but not to preclude thepresence or addition of further features in various embodiments of theinvention. Further, any method steps recited in the claims are notnecessarily intended to be performed temporally in the sequence written,or to be performed without pause once started, unless the contextrequires it.

It is to be understood that, if any prior art publication is referred toherein, such reference does not constitute an admission that thepublication forms a part of the common general knowledge in the art, inAustralia or any other country.

1. An air-conditioner for maintaining a temperature of a conditionedspace at or near a set temperature, the air-conditioner comprising: atleast one rotating or reciprocating element adapted to rotate orreciprocate at a variable frequency, the variable frequency includingone or more nuisance frequencies being frequencies at which vibration ornoise within the air-conditioner or the conditioned space causes anuisance; and a processor programmed to control variation of thevariable frequency in response to operational requirements; wherein theprocessor is configured to operate the at least one rotating orreciprocating element so as to substantially exclude operation at theone or more nuisance frequencies
 2. The air-conditioner of claim 1wherein the at least one rotating or reciprocating element comprises avariable frequency compressor supplying corresponding variablecompressive power.
 3. The air-conditioner of claim 2 wherein theprocessor comprises an adjustment capability allowing reconfiguring tosubstantially exclude operation at one or more of the nuisancefrequencies that are identified after manufacture of theair-conditioner.
 4. The air-conditioner of claim 3 wherein theadjustment capability allows reconfiguring to substantially excludeoperation at one or more of the nuisance frequencies that are identifiedafter installation of the air-conditioner.
 5. The air-conditioner ofclaim 1, wherein the processor is adapted to operate the at least onerotating or reciprocating element at a set of allowed frequencies whichdo not include any of the one or more nuisance frequencies and to causetransition between the allowed frequencies in response to theoperational requirements.
 6. The air-conditioner of claim 5 wherein thetransition is a programmed gradual transition between the allowedfrequencies over a transition time, avoiding operation at or within thenuisance frequencies for more than a maximum time during the transition.7. The air-conditioner of claim 6 wherein the maximum time is less than20 seconds.
 8. The air-conditioner of claim 7 wherein the maximum timeis less than 10 seconds.
 9. The air-conditioner of claim 8 wherein themaximum time is less than 5 seconds.
 10. The air-conditioner of claim 4wherein the processor is adapted to operate the variable frequencycompressor.
 11. The air-conditioner of claim 1, wherein the processor isadapted: to compute a target frequency for sustained operation accordingto the operational requirements; to compute a revised target frequencyby increasing or decreasing the target frequency if required to avoidthe one or more nuisance frequencies; and to operate the at least onerotating reciprocating element at the revised target frequency.
 12. Theair-conditioner of claim 11, wherein the processor is adapted toincrease the target frequency if required to avoid the one or morenuisance frequencies if a rate of change of temperature difference froma temperature set point indicates more power is required, and todecrease the target frequency if required to avoid the one or morenuisance frequencies if the rate of change of temperature differencefrom a temperature set point indicates less power is required.
 13. Theair-conditioner of claim 3 wherein the adjustment capability is providedby a capability of user to edit or add to a list of the one or morenuisance frequencies stored in a non-volatile memory.
 14. Theair-conditioner of claim 13 wherein the processor comprises a nuisancefrequency determination mode whereby the processor operates the rotatingor reciprocating element at one or more specific frequencies to allowobservation or measurement of whether the nuisance occurs during theoperation at each of the one or more specific frequencies.
 15. Theair-conditioner of claim 13 wherein: in the nuisance frequencydetermination mode, the processor is further adapted to receive input bythe user of the observation or measurement and to update the list of theone or more nuisance frequencies stored in the non-volatile memory. 16.The air-conditioner of claim 1, wherein the at least one rotatingreciprocating element comprises a rotating fan configured to supplyconditioned air or to pass air over a heat exchanger.
 17. Theair-conditioner of claim 1 wherein the air-conditioner is implemented ona recreational vehicle.
 18. A method of reducing a nuisance caused by anair-conditioner, the air-conditioner being adapted to maintain atemperature of a conditioned space at or near a set temperature, theair-conditioner comprising: at least one rotating or reciprocatingelement adapted to rotate or reciprocate at a variable frequency, thevariable frequency including one or more nuisance frequencies beingfrequencies at which vibration or noise within the air-conditioner orthe conditioned space causes a nuisance; and a processor programmed tocontrol variation of the variable frequency in response to operationalrequirements; the method comprising the step implemented in theprogrammed processor of operating the at least one rotating orreciprocating element so as to substantially exclude operation at theone or more nuisance frequencies.